Radio receivers such as AM and frequency modulation (FM) receivers are well known and are pervasive. Conventionally, these receivers have been formed of analog circuitry to receive an incoming radio frequency (RF) signal, downconvert the signal, and demodulate the downconverted signal to obtain an audio signal for output. Typically, the circuitry for AM and FM receivers, even in a combined radio, includes separate dedicated paths for AM and FM operation. While such analog-based circuitry may perform well, the area associated with this analog circuitry typically exceeds that used for digital circuitry, and the analog receivers typically include many discrete components. In contrast, digital circuitry is generally available in ever-decreasing sizes, as the benefits of advanced semiconductor processes provide for greater integration benefits. Furthermore, the cost of digital integrated circuits (ICs) is generally less than corresponding analog circuitry.
Accordingly, some radio receivers are being designed to incorporate greater amounts of digital circuitry. While such circuitry may improve performance and can be formed in small packages, typically there are complexities in processing RF signals that require significant digital processing to match the relatively simple circuitry of an analog receiver.
Additional issues exist in radio receivers. One such issue is finely tuning to a desired frequency. To effect such fine tuning, many receivers include an automatic frequency control (AFC) circuit to receive a feedback signal from a downconverted incoming signal in an effort to finely tune a local oscillator (LO) that is used to downmix the incoming signal to the desired frequency. Typically such AFC circuitry is present in a front end of the receiver to receive an output of the downconverting mixer and, via the action of feedback, attempts to finely tune the LO to obtain the desired channel frequency. However, this circuitry raises complexity and consumes additional circuit area and power.